Bottom Line:
We further show the admolecule motion on the zigzag-edged GRND is faster than that on the armchair-edged GRND with the same width and at the same temperature.These results can be well explained by analysing the potential energy surfaces of the systems.Since such hydrogenated graphene nanostructures have been experimentally realized, our results provide a valuable reference for constructing molecular conveyor circuits.

ABSTRACTWe study molecular mobility on a graphene nanoroad (GNRD), a pristine graphene strip embedded in between two hydrogenated graphene domains serving as a nanoscale pathway for transporting admolecules. Our molecular dynamics simulations using a prototype physisorbed C60 admolecule demonstrate that the proposed GNRD is able to confine the diffusive motion of the admolecule within the nanoroad up to a certain temperature, depending on its width and edge type. Within the confinement regime, the width and edge-type of the GNRD also play an important role in the molecular motion. Specifically, when the GNRD width is narrower than the admolecule diameter, the admolecule performs one-dimensional hopping motion along the nanoroad. When the GNRD width is larger than the admolecule diameter, the admolecule moves only along one of its edges at low temperatures, and shuffle between two edges at high temperatures. We further show the admolecule motion on the zigzag-edged GRND is faster than that on the armchair-edged GRND with the same width and at the same temperature. These results can be well explained by analysing the potential energy surfaces of the systems. Since such hydrogenated graphene nanostructures have been experimentally realized, our results provide a valuable reference for constructing molecular conveyor circuits.

f4: Potential energy surface (PES) of the C60 on (a) the 5‚ÄČ√Ö armchair-edged GNRD, and (b) the 4‚ÄČ√Ö zigzag-edged GNRD. (c,d) The energy profiles along the central line (y‚ÄČ=‚ÄČ0) of the GNRDs in (a,b) respectively. (e,f) The PES of the C60 on the GNRD with a width of about 20‚ÄČ√Ö and different edge types: (e) armchair, and (f) zigzag. In (e,f), due to the symmetry of the systems in the y direction (perpendicular to the edges), only half of the PES is presented, that is, .

Mentions:
First, we examine the trajectories of the C60 centre of mass (COM) on the armchair-edged GNRD at different temperatures. Simulation results are shown in Fig. 1, in which the C60 COM trajectory is presented in red, the hydrogen atoms are presented with blue circles, and the graphene honeycomb structure is presented in green. The left side panels (Fig. 1(a2‚Äďa4, , )) show the C60 trajectories on a 5‚ÄČ√Ö width armchair-edged nanoroad at 100‚ÄČK, 200‚ÄČK, and 300‚ÄČK, respectively. These trajectories illustrate that a 5‚ÄČ√Ö width nanoroad, which is narrower than the diameter of the C60 admolecule (with the mean atom-to-atom diameter of ~7.1‚ÄČ√Ö)29, is able to confine the surface diffusion of the C60 along the nanoroad up to the room temperature. The right side panels (Fig. 1(b2‚Äďb4)) show the typical trajectories of the C60 admolecule on an armchair-edged nanoroad with a width of ~20‚ÄČ√Ö at 100‚ÄČK, 200‚ÄČK and 300‚ÄČK, respectively. It is seen that the nanoroad, which is wider than the diameter of the admolecule, can also confine the molecular motion up to the room temperature. However, depending on temperature, the confined motion in this case shows two distinct regimes: At low temperatures (see Fig. 1(b2)), the C60 admolecule diffuses only along one of the edges. In this regime, the diffusion of the admolecule along the edge is via the hopping mechanism between the adjacent adsorption sites of the edge. This indicates that the edge of the GNRD plays the role as an ‚Äúadsorbing-wall‚ÄĚ in the motion of the admolecule. At high temperatures, the C60 admolecule ‚Äúswitches‚ÄĚ its motion between the two edges of the GNRD (See Fig. 1(b3,b4)). It can be seen that in this ‚Äúswitching‚ÄĚ motion, the duration of sticking intervals is reduced and the admolecule exhibits a quasi-continuous Brownian motion along the nanoroad edges. Our simulations show that the transition temperature between these two regimes for the armchair-edged GNRD occurs at around 150‚ÄČK. The physics behind the scene of adsorption of the C60 admolecule to the edges of a GNRD will be discussed later.

f4: Potential energy surface (PES) of the C60 on (a) the 5‚ÄČ√Ö armchair-edged GNRD, and (b) the 4‚ÄČ√Ö zigzag-edged GNRD. (c,d) The energy profiles along the central line (y‚ÄČ=‚ÄČ0) of the GNRDs in (a,b) respectively. (e,f) The PES of the C60 on the GNRD with a width of about 20‚ÄČ√Ö and different edge types: (e) armchair, and (f) zigzag. In (e,f), due to the symmetry of the systems in the y direction (perpendicular to the edges), only half of the PES is presented, that is, .

Mentions:
First, we examine the trajectories of the C60 centre of mass (COM) on the armchair-edged GNRD at different temperatures. Simulation results are shown in Fig. 1, in which the C60 COM trajectory is presented in red, the hydrogen atoms are presented with blue circles, and the graphene honeycomb structure is presented in green. The left side panels (Fig. 1(a2‚Äďa4, , )) show the C60 trajectories on a 5‚ÄČ√Ö width armchair-edged nanoroad at 100‚ÄČK, 200‚ÄČK, and 300‚ÄČK, respectively. These trajectories illustrate that a 5‚ÄČ√Ö width nanoroad, which is narrower than the diameter of the C60 admolecule (with the mean atom-to-atom diameter of ~7.1‚ÄČ√Ö)29, is able to confine the surface diffusion of the C60 along the nanoroad up to the room temperature. The right side panels (Fig. 1(b2‚Äďb4)) show the typical trajectories of the C60 admolecule on an armchair-edged nanoroad with a width of ~20‚ÄČ√Ö at 100‚ÄČK, 200‚ÄČK and 300‚ÄČK, respectively. It is seen that the nanoroad, which is wider than the diameter of the admolecule, can also confine the molecular motion up to the room temperature. However, depending on temperature, the confined motion in this case shows two distinct regimes: At low temperatures (see Fig. 1(b2)), the C60 admolecule diffuses only along one of the edges. In this regime, the diffusion of the admolecule along the edge is via the hopping mechanism between the adjacent adsorption sites of the edge. This indicates that the edge of the GNRD plays the role as an ‚Äúadsorbing-wall‚ÄĚ in the motion of the admolecule. At high temperatures, the C60 admolecule ‚Äúswitches‚ÄĚ its motion between the two edges of the GNRD (See Fig. 1(b3,b4)). It can be seen that in this ‚Äúswitching‚ÄĚ motion, the duration of sticking intervals is reduced and the admolecule exhibits a quasi-continuous Brownian motion along the nanoroad edges. Our simulations show that the transition temperature between these two regimes for the armchair-edged GNRD occurs at around 150‚ÄČK. The physics behind the scene of adsorption of the C60 admolecule to the edges of a GNRD will be discussed later.

Bottom Line:
We further show the admolecule motion on the zigzag-edged GRND is faster than that on the armchair-edged GRND with the same width and at the same temperature.These results can be well explained by analysing the potential energy surfaces of the systems.Since such hydrogenated graphene nanostructures have been experimentally realized, our results provide a valuable reference for constructing molecular conveyor circuits.

ABSTRACTWe study molecular mobility on a graphene nanoroad (GNRD), a pristine graphene strip embedded in between two hydrogenated graphene domains serving as a nanoscale pathway for transporting admolecules. Our molecular dynamics simulations using a prototype physisorbed C60 admolecule demonstrate that the proposed GNRD is able to confine the diffusive motion of the admolecule within the nanoroad up to a certain temperature, depending on its width and edge type. Within the confinement regime, the width and edge-type of the GNRD also play an important role in the molecular motion. Specifically, when the GNRD width is narrower than the admolecule diameter, the admolecule performs one-dimensional hopping motion along the nanoroad. When the GNRD width is larger than the admolecule diameter, the admolecule moves only along one of its edges at low temperatures, and shuffle between two edges at high temperatures. We further show the admolecule motion on the zigzag-edged GRND is faster than that on the armchair-edged GRND with the same width and at the same temperature. These results can be well explained by analysing the potential energy surfaces of the systems. Since such hydrogenated graphene nanostructures have been experimentally realized, our results provide a valuable reference for constructing molecular conveyor circuits.